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Received: from DESKTOP-5N7EMDA(mailfrom:ying.huang@linux.alibaba.com fp:SMTPD_---0XETU7Hc_1794274879 cluster:ay36) by smtp.aliyun-inc.com; Tue, 10 Nov 2026 09:41:19 +0800 From: "Huang, Ying" To: Zhiteng Qiu Cc: David Hildenbrand , Andrew Morton , Zi Yan , Matthew Brost , Joshua Hahn , Byungchul Park , Gregory Price , Alistair Popple , Xin Hao , Dave Hansen , Yuan Zhong , Shifei Ge , Jianyong Wu , Shijie Huang , Yibin Liu , Fengyu Wang , , Subject: Re: [PATCH v3] mm/migrate: don't batch the TLB flush when there is nothing to batch In-Reply-To: <20261110001816.2186986-1-qiuzhiteng@hygon.cn> (Zhiteng Qiu's message of "Tue, 10 Nov 2026 00:18:16 +0800") References: <20261106041628.1177963-1-qiuzhiteng@hygon.cn> <20261107143456.1590658-1-qiuzhiteng@hygon.cn> <20261109122915.2150586-1-qiuzhiteng@hygon.cn> <20261110001816.2186986-1-qiuzhiteng@hygon.cn> Date: Tue, 10 Nov 2026 09:41:18 +0800 Message-ID: <8733t9v4xt.fsf@DESKTOP-5N7EMDA> User-Agent: Gnus/5.13 (Gnus v5.13) X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Stat-Signature: bj3r1c1xus4hmqiob4jk3gk6s6zufnsg X-Rspamd-Server: rspam01 X-Rspam-User: X-Spam-Status: No, score=-14.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,UNPARSEABLE_RELAY, USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL autolearn=no autolearn_force=no version=4.0.1 X-Rspamd-Queue-Id: CA086100005 X-HE-Tag: 1794274884-76834 X-HE-Meta: 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 FltllNki LfHjIqI2cFI/DjSsUmQDziq0sMG1TnQw/xQb/R1WLWupLAV51Kth6vUezuKOhXzMIbqDBt8oooRGb3MCJzTEqCkgNm5+UxJo5FjrB9FIdBQ2OP96KeZXYbRNS+vKtOwu8qb0Q2kMazjXxSa2jriF+Ke2vezT0kTU9fIa1ZEEI/aU3OmGsew+Ml6pWvFrgvIZVReaQaaKuGThuYBQOiCUMp4qGfS3WgAv8owTY/xMvwgTA0TC9P6zodJGOT4UsjcDrvDFqYzFWUQ6NFjbojjYc6oSRfHZ/8phBDXCI3ZmvP5ojRNPo/ngd7Y1C+xEQmMdq+Lq30QiApbkzHpbBDnpapq3gzlbvIcxZluzB Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 Zhiteng Qiu writes: > On 11/9/26 14:07, David Hildenbrand (Arm) wrote: [snip] >> I am not quite happy about the folio_mapcount() check, though: as soon as we >> optimize try_to_unmap() to batch better for large folios, it would be just plain >> wrong. > > That makes sense. A large folio's mapcount alone would not tell us > how many separate flushes are needed once its PTEs can be handled > in a batch. > > Would it make sense to restrict the optimization to a single, > singly mapped small folio and keep batching for all large folios, > as in the scope of v2? The changelog performance numbers were > measured with the v2 check. Or do you have a different direction > in mind? If there's any behavior change, please rerun the test to verify. It's fine to reuse the result data if they are similar enough. > > Moving the check to the caller would read the mapcount before > locking the folio. My understanding is that a concurrent change > could only affect which flush path is chosen, and both paths are > correct. Please let me know if I'm missing a concurrency concern. > > Ying, since you suggested using folio_mapcount(), would you be > comfortable with limiting the optimization to small folios? I'm OK with it. Thanks to David for pointing out that folio_mapcount() isn't good here because we will optimize large folio tlb flushes. [snip] --- Best Regards, Huang, Ying